Method of modifying integral steam chest steam turbines

Abstract

A method of eliminating cracking between a steam turbine casing and a welded integral steam chest includes removing the integral steam chest from the steam turbine casing and replacing it with a separate and spaced apart steam chest having a plurality of steam exit ports. Steam inlet diffusers located in the turbine casing and normally connected to steam passageways in the integral steam chest are each connected to a corresponding steam exit port in the spaced apart steam chest. The connection between the spaced steam chest and the turbine casing is made by a plurality of relatively flexible steam pipes. Preferably, the integral steam chest is removed by cutting away the welded junction between the turbine and steam chest at a level corresponding to a radially outer end of the inlet diffusers in the turbine casing. The diffusers are each re-bored to a uniform diameter suitable for insertion of the flexible steam pipes. Each steam pipe is then welded to a corresponding diffuser. The separate spaced apart steam chest may be held in its spaced apart relation to the turbine casing by a relatively thin wall support member welded to the turbine casing. Steam control valves are preferably incorporated in each of the steam exit ports of the spaced apart steam chest and coupled to control means for controlling the admission of steam into the turbine casing.

What is claimed is: 
     
       1. A method of eliminating cracking between a steam turbine casing and an integral steam chest welded thereto, the integral steam chest having a plurality of steam passageways communicating with a corresponding number of steam inlet diffusers in the casing, the method comprising the following steps of: removing the integral steam chest from said steam turbine casing;   replacing the integral steam chest with a separate and spaced apart steam chest having a plurality of steam exit ports; and   connecting each exit port of the separate and spaced apart steam chest to a corresponding inlet diffuser in the turbine casing by means of a plurality of relatively flexible steam pipes.   
     
     
       2. The method according to claim 1 wherein the step of removing the integral steam chest comprises cutting away the welded junction of the integral steam chest to turbine casing at a level corresponding to a radially outer end of the inlet diffusers. 
     
     
       3. The method of claim 2 and including the step of boring each inlet diffuser to a uniform diameter suitable for insertion of the steam pipes therein. 
     
     
       4. The method of claim 3 and including the step of welding each steam pipe to the corresponding diffuser. 
     
     
       5. The method according to claim 1 further comprising the step of supporting the separate and spaced apart steam chest in spaced apart relation to the casing by a relatively thin wall support member welded to the turbine casing. 
     
     
       6. The method of claim 1 and including the steps of: placing a steam control valve in each steam exit port of the separate and spaced apart steam chest;   coupling at least part of the valves to control means independent of the control means of the remainder of the valves; and   operating the control means to vary the valve positioning for smooth transition between different partial-arc operating conditions.   
     
     
       7. The method of claim 6 wherein the control means comprises cam actuating means, the step of operating including the step of selectively actuating the cam actuating means to control valve position.